Photonic Filter for THz via Optical Injection Into a Feedback-Controlled On-Chip Multi-Wavelength Laser

The growing demand for ultra-fast wireless data transmission is accelerating the exploration of THz frequencies for next-generation wireless communication systems. THz photonics provides a platform for generating, processing, and detecting THz signals by upconversion to the optical domain and leveraging the large available bandwidth of photonic devices at optical frequencies. However, efficient, tunable, and agile photonic filters remain a significant technical challenge. Here, we present a monolithically-integrated, feedback-controlled multi-wavelength laser (MWL) enabling photonic filtering through regenerative amplification induced by optical signal injection. The feedback cavity enables agile control of the filter response by tuning the feedback phase. We experimentally demonstrate selective filtering of an upconverted THz signal comprising two channels separated by 34 GHz and offset by 1.3 THz from the carrier. Using a broadband signal, our photonic filter achieves up to 20 dB suppression ratio, 3-dB bandwidths as narrow as 160 MHz, and optical gain of up to 15 dB for signals with optical power levels commonly obtained after THz-to-optical conversion, making it highly attractive for THz communication links.